1. Technical Field
The present invention pertains to the field of cellular communication. More particularly, the present invention pertains to wireless transmission of point-to-multipoint data (e.g. MBMS data) to mobile stations and cell changes of mobile stations in connection with such transmissions.
2. Discussion of Related Art
MBMS (Multimedia Broadcast/Multicast Service) is a unidirectional point to multipoint (p-t-m) bearer service in which data is transmitted from a single source entity to multiple recipients. MBMS is used to provide for example streaming video and audio.
An example of MBMS is that provided by GPRS (General Packet Radio Service) of a GSM (Global System for Mobile Communications)/EDGE (Enhance Data rate for GSM Evolution (EDGE) radio access network (GERAN). The Third Generation Partnership Program Technical Specification 3GPP TS 43.064 contains an overview of the GPRS radio interface (Um reference point). 3GPP TS 43.051 is an overall description of the GSM/EDGE Radio Access Network (GERAN) in so-called Iu mode.
For some cellular communication systems (such as GSM), a mobile station acquiring an MBMS session on a p-t-m channel provided by a network implementing a cellular communication system, if polled by the network, is configured to report an acknowledgement message giving the status of data received for the session up until the mobile station is so polled (as set out in 3GPP TS 43.246 and 3GPP TS 44.060). Such status information is used by the network to trigger retransmissions of data blocks not received by some mobile stations.
A mobile station is also expected (at least in some networks) to report up to the six strongest non-serving carriers to the network in a single acknowledgement message. The reporting of non-serving carriers is used by the network to allow for prioritizing the transmission of MBMS Neighboring Cell Information (MNCI) messages for cells indicated as most likely targets for cell changes by mobile stations, over those for cells that are less likely targets. This increases the chances that a mobile station has received neighboring cell p-t-m parameters for a given session for a cell—which parameters are included in the MNCI and which it needs in order to receive the MBMS session in the cell—before it changes to the cell, so the mobile station can quickly continue acquiring the session after cell change to the cell.
In order for a mobile station to access a target cell, the cell reselection parameters of the target cell must be known by the mobile station. Well-known so-called SI2n messages are scheduled by the network in a serving cell to provide such information for a target cell, as opposed to letting the mobile station tune to the target cell and thereby acquire the parameters.
Thus, a mobile station receiving an MBMS session in one cell and in a situation where it is likely that the mobile station should change to a new cell to continue the session, must know the corresponding p-t-m parameters for the new cell and also the cell reselection parameters for the new cell. It would be advantageous for a mobile station to cooperate with the network to ensure that the mobile station has such p-t-m parameters and cell reselection parameters.